The disclosed technology relates to chlorinated polyvinyl chloride (CPVC) compounds being free of heavy metals, particularly heavy metals in the form of stabilizer additives, the most common heavy metal being tin.
Halogen containing polymers tend to degrade or deteriorate when processed. Generally, the difference between the processing temperature and the degradation temperature is very small and there is a risk that the halogen containing polymers will therefore degrade. When such polymers degrade, it is believed that the halide acid generated by the polymer attacks the components of the processing equipment. Also, this acid further catalyzes elimination reactions and additional degradation of the polymer.
Stabilizers have been developed to help deter such degradation. For example, heavy metal compounds such as tin are commonly used as heat stabilizers. However, heavy metal stabilizers are becoming disfavored as heat stabilizers for halogenated polymers due to environmental concerns. As a potential replacement, organic based stabilizers (OB-Stabilizers) have been developed to stabilize halogen containing polymers. First generation OB-Stabilizers have been uracil based.
For example, EP1044968B1 to Chemtura Vinyl Additives teaches the use of uracil derivatives having the general formula I for the stabilization of chlorine-containing compounds.
The EP'968 patent teaches that zeolites can be employed in combination with the uracil derivatives of formula I in amounts of about 0.1 to 20 down to about 0.1 to 5 parts by weight, based on 100 parts by weight of the chlorine-containing polymer. The EP'968 patent also teaches that alkali and alkaline earth metal compounds, such as carboxylates, can be employed with the uracil derivative stabilizers. The preferred chlorine-containing polymer taught in the EP'968 patent is polyvinyl chloride (PVC). The patent does not teach or exemplify a formulation including CPVC.
U.S. Pat. No. 3,436,362, to Hayer et al., issued Apr. 1, 1969 teaches a stabilized polymer composition having between 0.1 and 10 parts by weight of stabilizer per 100 parts by weight of polymer. The stabilizer is uracil and its derivatives of general formula below and the polymer can be a halogenated vinyl compound, and specifically PVC.

U.S. Pat. No. 4,656,209, to Wehner et al., issued Apr. 7, 1987 teaches a thermoplastic molding composition based on vinyl chloride polymers containing 0.1 to 5% by weight of an aminouracil of formula I. The patent further teaches that additional amounts of conventional PVC stabilizers may be employed, such as metal carboxylates. Zeolite is not mentioned and the patent does not teach or exemplify a formulation containing CPVC.

U.S. Pat. No. 5,859,100, to Wehner et al., issued Jan. 12, 1999 teaches compositions including a rigid or semi-rigid PVC having a plasticizer content of up to 20%, and at least one aminouracil derivative compound of formula 1. Zeolites are expressly excluded and the patent does not teach or exemplify a formulation containing CPVC.

International application WO 2008/023249 to Chemfit Specialty Chemicals teaches a composition including an organic based stabilizer, such as uracil and its derivatives, and a smoke suppressant. Zeolites and carboxylates are disclosed as suitable smoke suppressants. The publication does not teach or exemplify a formulation containing CPVC.
The art above is directed more toward PVC type polymers than CPVC compositions. While zeolite and carboxylate may be suitable as co-stabilizers in the PVC stabilizer combinations taught, it would not be readily apparent that the same combinations would apply to CPVC compositions.
More specifically, where heat stabilizers protect the backbone of a halogenated polymer from degrading, acid scavenger co-stabilizers prevent the loss of halogen, such as chlorine, in the form of acids, such as HCl. PVC and CPVC resins are distinctly different polymers, most particularly in the level of chlorine present in the compositions. The higher level of chlorine in CPVC resins requires different handling than PVC. For example, the higher processing temperatures required to process CPVC also require a more robust stabilizer formulation to protect the CPVC. Thus, it is not directly obvious that what will work for processing PVC formulations will work for CPVC formulations.
It would be beneficial to the industry to prepare an inexpensive and readily available alternative to current stabilizer systems for CPVC resins.